


will forever be enough?

by blackorchids



Category: Life with Derek
Genre: Babies, Communication, Doggy Style, Domestic Fluff, Established Relationship, F/M, Family, Family Feels, Fluff, Fluff and Smut, Future Fic, Intimacy, Nonverbal Communication, Oral Sex, Post-Canon, Tumblr Prompt
Language: English
Status: Completed
Published: 2018-05-27
Updated: 2018-05-27
Packaged: 2019-05-14 14:30:41
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,390
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/14771447
Author URL: https://archiveofourown.org/users/blackorchids/pseuds/blackorchids
Summary: It's not like Derek didn't already expect to spend the rest of his life with Casey, okay? Simon just helped him imagine it a little more viscerally.





	will forever be enough?

**Author's Note:**

> what is it with me and established!relationship fic lately??
> 
> title from jason derulo's _marry me_ which is the sweetest fucking song you guys
> 
> prompt from anon: hope you love it my dude

At this point, it’s pretty easy to ignore the long-familiar lurch that is his belly jumping into his throat when he watches Casey sweep her long hair over one shoulder and lean down over Simon’s math worksheet to help him figure out the answer to one of the questions. It had been harder when the sensation was newest: when he’d watched Casey moving around the kitchen with Marti on her hip, easily, naturally, never hesitating no matter how much Marti’s wild creativity had annoyed her.

By the time Nora had had Simon, Derek had expected to be expert level in swallowing down the realization that Casey would be a good mom, that he maybe wanted to help her become that, but watching her back then, with their tiny, _shared_ baby brother, her shorter, blonder hair falling in her face as she looked down at him, her longer, curlier hair pulled back as she bent nearly in two to let Simon hold her fingers in two grubby fists as he took some of his first steps, her eyes lit up with warmth when she and Simon and Marti huddled in a pile as she read politically correct fairytales out loud. Marti had protested that she was too old for bedtime stories, but she hadn’t left the circle of Casey’s arms, because she was easily the smartest of the five original blended-family children.

So, it had been a new set of skills required to handle adult Casey with the growth and development of an actual baby, but Simon’s nearly six and Derek’s heart skipping a beat when he watches them together is practically part of his personality: hockey nut, film geek, college senior, secret president of the Casey fanclub.

“Der, Marti’s dance class,” Casey reminds him, because she thinks he’s mindlessly watching the baseball game on the television, and Derek lets her continue to think that, grumbling and groaning for show as he climbs out of the—honestly decrepit—chair he’s still managed to get dad and Nora to keep.

He’s early picking Marti up from dance practice, so he goes inside to wait on the benches lining the perimeter of the studio space with all of the moms who watch each lesson. Marti spots him when she’s bent in a terrifyingly twisted shape and waves, her grin wide even as her head is upside down. Her coach takes them through some actually-helpful stretching exercises at the end of the lesson and Marti, teenager that she is, doesn’t head directly over to Derek when they break, instead choosing to smile and laugh with a few girls on the team.

She touches a hand to Jada’s elbow and tucks her hair behind her ear with her free hand and Derek’s mouth drops open when he realizes it’s some freakish combination of his and Casey’s best flirting moves. Jada blushes and a distant part of Derek thinks _go, Marti!_ while the rest of him is trying to compute that, not only is his sister apparently now old enough to be flirting, but she’s _learned how to_ from. Him. And Casey.

Eventually, Marti comes his way, a blushing girl in her wake, and she gives Derek a _look_ , like she knows he’s having a crisis.

“I need ice cream,” Marti says, because she’s picked up some of Casey’s kindness, but once he’s paid, she’s narrowing a too-shrewd gaze on him because she’s also picked up Lizzie’s intuition.

Derek more or less unsuccessfully avoids Marti’s questions and it’s only when Casey texts her asking whether they’ve gotten lost is he able to hustle her back to the car so they can get back to dad and Nora’s.

Dinner is at once familiar and foreign, the way it’s felt since the first time he and Casey had come back from college to discover that there had been a new dinner table and, with it, new dinner seating. Lizzie’s shaved half her head and looks pretty badass, Edwin’s trying to grow a beard and looks pretty homeless. Nora and dad look far less stressed now that four of their children don’t live in the house full-time, and Derek would feel guilty about that, but he knows no one’s trying to get him to apologize.

The conversation is convoluted and flowing, Edwin and Marti bickering, Lizzie throwing a roll at Derek, Simon shouting above everyone else what they’d done in gym class that day, and Derek loves where he and Casey are living now, loves the off-campus housing and the bustling college-town and the closeness to New York, but he’s pretty sure he’s going to have to move back to London after college. It’s a marked difference from the Derek who never wanted to have family time in high school, but Derek figures after three and a half years of college, the only thing that’s changed about him can’t possibly just be his hair.

Casey squeezes his hand under the table, and he guesses that she somehow knows what he’s thinking, because her smile is pleased and fond and just a little smug.

They allow themselves to be shuffled off to the basement suite with minimal protest, another change in the family order making everything feel a little whip-lashy, but Simon had gotten Derek’s old room and Nora and his dad had wanted to be closer to him when he was younger.

The tv in the basement is a little old, but it’s late anyway so they keep it on mute, playing Stephen Colbert reruns and Casey smirks at him a little, because in all their years of knowing each other, she’s picked up a little of his inherent evil.

Not enough, because when Derek finally says it outloud, her mouth falls open in surprise.

“Wh—what?” Casey demands, her voice not much louder than a breath.

“Let’s make a baby,” Derek says, enunciating a little to try and sound cockier than he feels. Casey reaches out for his hand and he lets her pull him towards the bed.

“I mean,” Casey’s saying, voice a little higher than normal even as she starts automatically trying to pull off his hoodie. “We’d have to talk about this—and it would take a while for my birth control to be out of my system—we probably wouldn’t even get pregnant straight away anyway—this is a _huge_ step—”

Derek lets her keep talking and undressing him, is unbearably fond of her neuroticism, pushes her back onto the bed until her hair is fanned out around her head, kisses her on her jaw and down her neck so she can keep up the nervous rambling that means she’s trying to talk herself out of her kneejerk agreement, because Casey’s changed _a lot_ , nearly as much as him, but he knows she still has to convince herself an idea is a good one, even if she wants it really badly.

Casey’s voice fizzles out when Derek thumbs at the clasp of the bra she’s still wearing underneath her pajamas: thin, cotton, frumpy, _adorable_ , even if he still denies having that word in his vocabulary. 

“No, don’t let me interrupt,” Derek says and she gets a look on her face like she’s going to ask if he’s an alien imposter, but her leg tightens around his waist and one of her hands sweeps across the curve of his back to cup at the nape of his neck.

“You want to have a baby?” Casey asks instead of reverting back to mindless rambling. She uses her free hand to stop fiddling with the waistband of his plaid pajama pants to cup his jaw, a little tighter than usual in her nerves. Her gaze is steady on his face as she repeats the question, more serious than they usually are in bed. “You want to have a baby with _me_?”

Derek turns his face a little so he can kiss her palm and her eyelashes flutter against her cheekbones at his somewhat uncharacteristic sentimentality. Derek has always known when to be gentle with her and when she needs to fight, but when they’d stumbled out of quote unquote accidental hooking up and into a real, genuine, grown-up relationship, he’d had to start learning how to let himself finally, _finally_ be intimate.

“Who else?” he asks rhetorically when she opens her eyes to gaze up at him some more, and her mouth twists a little, like she’s going to laugh, and Derek bends down to kiss her firmly before she can.

Casey having already mostly undressed the pair of them while she’d worked through everything proves to be helpful, because it’s just a few rolls of her hips before she’s got her pants off and she’s naked and eager beneath him, and he knows, even as he kisses her deeply, one of his hands smoothing up the side of her ribs so he can get his thumb on her nipple, that she’s going to want to have a _grown-up talk_ about all of this, because Casey reads a lot of self-help books and doesn’t want to admit that their unusual way of communicating is just as effective as sitting across from each other at a table with a list of discussion topics.

Derek’s honestly a little excited about it all.

Casey gets a hand around him and twists just on the far side of too-tight, digs her fingers into his shoulder blades, pushes his head down so he can put his mouth on her ignored breast, so he can bite his way down the valley between her breasts, so he can nip at her stomach, so he can leave a few bruises on her hips and thighs before she tugs his head to just where she wants him.

Derek licks one broad stroke from end to clit, scraping his teeth on the little bud cursorily, and Casey’s back arches a little, one of her legs kicking out so she can rest the back of her thigh against his shoulder and use the flat of her foot to keep him there.

Derek’s all too happy to be kept, uses one hand to brace against her hips and the other to get two fingers inside her, twisting and curling them upwards until she keens a little, never easing up on her clit. Casey’s giant brain needs a lot of forms of attention to keep her from getting a little too inside her head, and Derek’s always been up for the challenge, switches with ease between scraping his teeth against her inner thighs, alternates his fingers and his tongue without any sort of pattern.

Her first orgasm comes easily, but she still feels tense so he keeps going without scarcely a pause, and a quick glance up lets him know Casey’s picked her head up from the pillow so she can watch him, two fingers in her mouth and one hand on her breast like she’s made up of his personal fucking fantasies and Derek has to _force_ himself to stop staring and get back to it.

He circles around her entrance with the point of his tongue before flicking it inside, one thumb switching from rapidfire kitten strokes to slow-and-steady swipes over her clit, and Casey’s only ever really quiet when she’s in bed, so Derek relies on the familiar symphony of her hitched breaths and tiny vocalizations to let him know when she’s getting close and he needs to switch again.

“Der _ek_ , you ass,” Casey finally grits out, twisting her fingers in his hair _hard_ , and he switches for the last time, scissoring his fingers inside and pulling her clit between his lips so he can suck at it hard and fast until her leg spasms against his shoulder and he can feel her toes curling against his spine as she comes, huge silent sigh of pleasure escaping her while he works her through it.

Casey pulls him up to her, kisses him wet and deep like she’s trying to chase the taste of herself in his mouth for a long time before his absent rutting pulls her out of the haze long enough for her to twist around so she can press her face against her pillow and present him with her, honestly glorious, ass, a peek of her wet cunt between her legs tantalizing and all too tempting to resist.

Derek scrapes a hand from between her shoulder-blades over the curve of her spine to the small of her back, uses it to brace himself as he uses his other one to tug at himself a few times before he lines up and pushes in in one clean stroke.

Casey’s back arches almost immediately and she ruts back against him, eager for it but still letting him set the pace. One of her arms comes up to wrap around her pillow, and her other one sneaks between herself and the mattress to thumb at her clit.

Derek pulls out and pushes back in, sure and steady in a way that they’ve learned after years of exploring one another's’ bodies, but the sight of her hips rocking back for it and her arm moving as she plays with her clit while he fucks her is still a little overwhelming, in the best way, and he stoops a little bit over her because the both of them like being close when they’re doing it like this and can’t see each others’ faces, and soon enough Derek feels his balls tighten up and he’s tightening his grip on Casey’s hip as he pushes in one last time before he feels his orgasm yanked out of him from somewhere deep, feels it pulsing behind his eyes and beneath his belly and tingling at his fingertips as she bears down on him and lets him work himself through it.

He pulls out when he’s caught his breath a little and the absense of the condom makes his insides light up like fireworks just at the thought of it: soon enough, after their _very grown-up discussion_ , Casey’s going to stop the birth control and they’re going to be trying for a baby.

Derek pulls her atop him when he collapses next to her on the mattress, wraps a hand around her waist in such a way that he can brush his fingers against her stomach, still flat, but brimming with potential.

**Author's Note:**

> come talk to me on [tumblr](http://www.rosalinesbenvolio.tumblr.com)!


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